Anisotropy of losses in amorphous ribbons

The soft magnetic properties of amorphous ribbons are expected to be anistropic because of the shear deformation during the melt spinning procedure. In this paper the losses of an Fe₈₀B₁₄Si₆ amorphous ribbon were measured on stripes which were cut either parallel or perpendicular to the ribbon axis. The dependence of the losses as a function of peak induction and frequency suggests that there is an easy axis of magnetization parallel to the ribbon axis. After stress relief annealing this anisotropy is reduced. That is why this anisotropy is assumed to be due to internal stress introduced upon quenching.     

外磁场与带轴夹角对非晶FeSiB/Cu/FeSiB三明治薄带巨磁阻抗特性的影响

采用层间胶合方法制备了淬态非晶FeSiB/Cu/FeSiB三明治薄带,研究了同尺寸单层薄带和三明治薄带的巨磁阻抗(giant magneto-impedance, GMI)随外磁场与带轴夹角β的变化特性.结果表明,FeSiB单层薄带在7.0 MHz最佳响应频率下,GMI仅约30%,外磁场与带轴夹角对单层薄带GMI几乎没有影响;三明治薄带的GMI效应则十分显著,在0.6 MHz最佳响应频率下,纵、横向GMI比分别达到272%和464%, GMI随β的增大而增强;所有β角的三明治薄带GMI曲线都出现各向异性峰,各向异性峰随β的增大而展宽.根据磁畴转动模型推导了薄带横向磁导率与各向异性场及β之间的函数关系式.结果显示,三明治薄带GMI随夹角β变化的特性与理论推算的横向磁导率变化有较好的一致性,而单层薄带则不然.该磁畴转动模型能定性解释三明治薄带GMI随外磁场方向变化特性.     

Tuning stress-induced magnetic anisotropy and high frequency properties of FeCo films deposited on different curvature substrates

It is important to control magnetic anisotropy of ferromagnetic materials. In this work, FeCo thin films are deposited on the curving substrates by electrochemical deposition to adjust the stress-induced magnetic anisotropy. The compressive stress is produced in the as-deposited films after the substrates are flattened. A simplified theoretical model of ferromagnetic resonance is utilized to measure the intrinsic magnetic anisotropy field and saturation magnetization. The results show that the stress-induced magnetic anisotropy and the resonance frequency increase with the increase of substrate curvature. The induced easy axis is perpendicular to the compressive stress direction.     

Magnetization reversal in amorphous ribbons studied by neutron depolarization

The magnetization process in an amorphous ribbon with an easy axis perpendicular to its plane has been studied with the three-dimensional neutron depolarization technique. A simplified model of three layers is used, describing the magnetization distribution in the bulk and the two closure domain structures at the surface. Our analysis with this model gives direct experimental evidence that the magnetization process due to an applied magnetic field in the ribbon plane is dominantly accounted for by rotation processes of the local magnetization in the bulk. The influence of different types of closure domain structures on the magnetization distribution during the reversal process are discussed and compared with the experimental results.     

铁磁/反铁磁双层薄膜中应力各向异性研究

采用铁磁共振方法,研究了铁磁/反铁磁双层薄膜中交换各向异性和应力各向异性对其物理性质的影响.结果表明,单向各向异性来源于界面交换作用,应力各向异性对材料的磁化难易程度有较大影响.当外磁场方向与应力场方向平行时,应力场的存在将促进该方向的磁化.反之,应力场将会阻碍该方向的磁化.     

Temperature-induced magnetic phase transitions in crystals with competing single-ion and interionic magnetic anisotropies

Temperature-induced phase transitions in a uniaxial ferromagnetic system of spins S = 1 with competing one-particle and two-particle anisotropies are studied. It is shown that, in the case where easy-plane single-ion anisotropy dominates over easy-axis two-particle anisotropy, the transition from the paramagnetic state to a ferromagnetic state with magnetization perpendicular to the anisotropy axis is a second-order displacive magnetic phase transition. In the opposite case, where two-particle anisotropy dominates over single-particle anisotropy, the transition to a ferromagnetic state with magnetization perpendicular to the anisotropy axis is also continuous but of the order-disorder type. In a system with competing second-order one-and two-particle anisotropies, the orientational first-order phase transition can occur to a state with the magnetization directed along or perpendicular to the anisotropy axis.     

Specific features in precession dynamics of magnetization of a uniaxial magnetic film

The precession dynamics of the magnetization of a film with in-plane uniaxial anisotropy in the case of its biasing along the hard magnetization axis has been analyzed by numerically solving the Landau-Lifshitz equations. It has been revealed that the ferromagnetic resonance spectrum near the magnetic anisotropy field exhibits an additional peak, which is associated with the angular bistability due to the presence of two symmetric angular equilibrium positions. The trajectories of precession motion during biasing along the hard magnetization axis differ substantially from the trajectories corresponding to the biasing along the easy axis.     

Magnetic behavior and domain structure in as-quenched, annealed, and stress-annealed CoFeCrSiB ribbons

Combination of magneto-optical (MO) vector magnetometry and magneto-optical Kerr microscopy is used to investigate the surface magnetic properties of amorphous CoFeCrSiB ribbons. Strongly inhomogeneous magnetic behavior of ribbons in as-quenched state is improved by field-annealing and stress-annealing processes that induce weak uniaxial longitudinal and transverse anisotropy. It was shown that values of coercive and anisotropy field increase with increasing annealing temperature. Inclination of easy axis from the ribbon axis is estimated by comparing the measured surface hysteresis loops with the Stoner–Wohlfarth model, and is supported also by the Kerr microscopy. Method with the current flowing through the ribbon is proposed for magnetic domains observations.     

Ferromagnetic Resonance Spectra in Single-Crystal Hexagonal Ferrites

Theoretical and experimental studies of ferromagnetic resonance in single-crystal hexagonal ferrites with different types of magnetocrystalline anisotropy (axis and plane of easy magnetization) are reported. The ferromagnetic resonance is examined in the 12–38 GHz frequency range in the state of homogeneous magnetization and in the presence of a strip domain structure inherent in materials with an axis of easy magnetization. This comprehensive ferromagnetic resonance investigation is shown to allow determination of not only anisotropy fields and g-factors but also saturation magnetization of a material from testing one sample alone. The anisotropy of g-factor of Zn₂Y is found experimentally.     

Study of rapid stress annealed nano-crystalline Fe74.5Cu1Nb3Si15.5B6 alloy

Rapid stress annealing induced changes in structural and magnetic properties in Fe_74.5Cu₁Nb₃Si_15.5B₆ are reported. Obtained results suggest changes in spin texture with preferred orientation along ribbon axis. Fraction of A site in the DO₃ lattice occupied by Si atoms, increases, with increase of applied stress during annealing. Volume fraction of the nanograins up to 60% (exhibiting quite similar mean grain diameter ～9 nm) is observed. Lattice parameter values suggest that Si content in the nanocrystalline phase is between 14% and 19% and increase of lattice parameter suggests the elongation of the unit cell. Studied stress annealed samples exhibit soft magnetic behavior (coercive field ranging between 4 and 8 Am^???1). Stress annealing reduces permeability whereas anisotropy field increases almost linearly exhibiting the induction of uniaxial and perpendicular to the ribbon axis anisotropy. Obtained stress-induced-anisotropy constant values range between 50 and 2,140 Jm^???3.     

Experimental study of regions of reversed magnetization in an amorphous layer of Co70Fe5Si10B15

The characteristics of the distribution of magnetization and remagnetization of microsections of the surface in the amorphous alloy Co₇₀Fe₅Si₁₀B₁₅, prepared in the form of thin ribbons, were studied by the magnetooptical method. It was found that the magnetization I on the surface of the amorphous ribbon studied was strongly nonuniform. It was established that heat treatment (HT) of the sample leads to the appearance of regions of reversed magnetization in the surface layer of the ribbon, while thermomagnetic annealing reduces the nonuniformity of I. The conservation of the transverse component in the HT sample in fields where the magnitude of the component of magnetization parallel to the length of the ribbon remains virtually unchanged suggested that a domain structure of the magnetization ripple type, owing to the strong microdispersion of the magnetic anisotropy, is realized in this sample.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 89–94, March, 1988.     

正交各向异性双层交换弹簧薄膜的磁矩分布

本文以Pt_(84)Co_(16)/TbFeCo双层交换弹簧体系为研究对象,利用微磁学连续模型,研究了软/硬磁层易轴方向相互垂直的新型体系中磁矩的分布特征.研究结果表明,磁矩偏离薄膜法线方向的角度在软磁层中沿膜厚方向的变化速率比硬磁层中的快.通过调节软磁层参数来增加软/硬磁的各向异性常数比、交换能常数比、饱和磁化强度比或外磁场强度,都可有效改变磁矩偏角在软/硬磁层中的变化速率.特别是当软/硬磁各向异性常数比值和交换能常数比值同时增大时,可以使得磁矩在硬磁层中的变化速率快于软磁层中的.而饱和磁化强度比值对磁矩变化速率的影响源于饱和磁化强度的变化会相应地改变各向异性常数,进而改变磁矩在软/硬磁层中磁矩方向变化速率的比值.此体系的磁滞回线显示磁性参数的改变可以显著改变体系的剩磁及饱和磁场.软磁层中的退磁场能及体系的正交各向异性可导致负的成核场.     

Spin reorientation transition in (111) textured L10 CoPt layers

In this work, a spin reorientation transition from [001] axis to an in-plane direction occurs near Curie temperature under a small external field for (111) textured L1₀ CoPt layers in an AlN/CoPt multilayer film, indicating the dominant role of the shape anisotropy at elevated temperatures over the magnetocrystalline anisotropy. A large in-plane residual magnetization is also observed after cooling the sample from a temperature above the Curie point. The formation of magnetization during cooling is considered due to the alignment of magnetic moments along the easy axis by the small field in the spin reorientation transition temperature region. Our work reveals the importance of shape anisotropy for the formation of magnetization in the heat assisted magnetic recording process.     

Magnetization and transport characteristics of layered high-temperature superconductors with different anisotropy parameters

The magnetization of a layered high-temperature superconductor with different anisotropy parameters has been calculated using the Monte Carlo method in the framework of a modified three-dimensional Lawrence–Doniach model with actual boundary conditions. The penetration of a magnetic flux into a bulk sample from the boundary has been simulated, and the curves of magnetization reversal of a high-temperature superconductor by an external magnetic field have been calculated for different anisotropy parameters γ and types of defects in the sample. It has been found that there are significant differences in the magnetization curves and transport properties of superconductors with different anisotropy parameters γ. The influence of tilted columnar defects on the critical current has been analyzed. A decreasing dependence of the critical current on the tilt angle of defects with respect to the c axis has been obtained. It has been shown that, as the anisotropy parameter increases, this dependence weakens and, for a specific value of γ, disappears. An explanation of the mechanism responsible for the disappearance of the dependence has been proposed.     

Double shifted magnetization curves in magnetic bilayers

Ultrathin ferromagnetic biaxial films exhibit uniaxial anisotropy induced by underlayer and double shifted magnetization curves. Two possible origins of the double shifted curves are identified from experimental data, namely, the step-induced anisotropy and the exchange-coupled induced interfacial anisotropy. Micromagnetic study of modified astroids with starlike shapes indicates that a large uniaxial anisotropy induced by the interface plays a key role in the formation of double shifted magnetization waves. An additional bias field along the easy axis may enhance the shifted field. The present research status, both experimental and theoretical, is briefly discussed.     

Micromagnetism in a planar system with a random magnetic anisotropy and two-dimensional magnetic correlations

The hysteresis loops and the micromagnetic structure of a ferromagnetic nanolayer with a randomly oriented local easy magnetization axis and two-dimensional magnetization correlations are studied using a micromagnetic simulation. The properties and the micromagnetic structure of the nanolayer are determined by the competition between the anisotropy and exchange energies and by the dipole–dipole interaction energy. The magnetic microstructure can be described as an ensemble of stochastic magnetic domains and topological magnetization defects. Dipole–dipole interaction suppresses the formation of topological magnetization defects. The topological defects in the magnetic microstructure can cause a sharper change in the coercive force with the crystallite size than that predicted by the random magnetic anisotropy model.     

Effects of compressive stress on a steel cube using tensor magnetization and magnetostriction analysis

Measurements of the effects of a compressive stress on magnetization and magnetostriction loops of a cubic sample from a steel pipe are presented. The compressive stress was applied perpendicularly to the magnetic field and, in order to take account of the anisotropy of the sample, measurements were performed in all three orthogonal directions with field applied successively parallel to each direction of the cube edges. This gives rise to 3×3 matrices defining the magnetization and magnetostriction tensors. Analysis of each element of the tensors enabled, firstly, the initial preferential orientation of the magnetic domains due to the texture to be identified and, secondly, permitted us to follow the changes in the bulk easy axis induced when the compressive stress was applied. Valuable information about these changes in the domain arrangements was obtained from analysis of the off-diagonal elements of the magnetization tensor.     

铁磁球/反铁磁纳米体系磁滞回线的Monte Carlo模拟

利用经典Heisenberg模型和Monte Carlo方法研究外磁场和反铁磁磁晶各向异性、交换相互作用对铁磁球均匀嵌入到反铁磁基体中的铁磁/反铁磁纳米体系磁滞回线的影响.模拟结果显示,外加反向最大磁场不同时,磁滞回线形状不同.当磁场正向增加时,体系的磁化强度会产生一个跃变,但跃变高度与反向场最大值无关.反铁磁磁晶各向异性越大,体系的交换偏置现象越明显,且磁化强度回到饱和值所需的外磁场越大.随着反铁磁基体交换相互作用的增大,在正向和负向磁场区域还可能出现新的磁滞现象.     

Ferromagnetic resonance study of the effect of elastic stresses on the anisotropy of magnetic films

The distribution of the magnitude and direction of the uniaxial magnetic anisotropy field over the area of permalloy films obtained by thermal evaporation in vacuum was studied using a scanning ferromagnetic resonance spectrometer. The films were deposited on glass substrates subjected to bending stress in the presence of an in-plane static magnetic field. Depending on the character of the elastic-stress distribution over a local spot of a film, the uniaxial anisotropy induced by a magnetic field is either enhanced or completely compensated, which is accompanied by a significant change in the direction of the easy axis of magnetization. The observed effects are in good agreement with phenomenological calculations.     

A simple induction anisometer

Magnetic anisotropy of rotationally symmetric samples is measured by a simple induction method based on transverse susceptibility measurements. The sample is magnetically saturated by a d.c. field perpendicular to the axis of rotation. A small a.c. field is applied in the direction perpendicular to both the d.c. field and the axis of rotation. The transverse a.c. susceptibility is measured by a Hartshorn bridge of mutual inductance. From the transverse susceptibilities along different directions the anisotropy constants as well as the saturation magnetization can be determined.